1. Field of the Invention
The present invention relates generally to disk drive write heads with pole tips that have reduced pole-tip erasure properties, and to methods of manufacturing such write heads.
2. Related Art
Disk drives are used in a wide variety of electronic devices, ranging from personal computers to portable media players, for the storage and retrieval of data. In a disk drive, data is typically written to and read from magnetic storage media called disks. A disk drive typically comprises a plurality of disks for the storage of data and one or more read/write heads for the reading and writing of data. There is a constant market demand to increase the data storage density of disks. Increasing the storage density of the disks can decrease the price to storage-capacity ratio of the disk drives, increase performance, and decrease the physical dimensions of the disk drive.
Traditionally, longitudinal recording has been used to record data on a disk drive. In longitudinal recording, the data bits are aligned parallel to the surface of the disk. Each bit is composed of a group of magnetic grains with magnetization aligned parallel to the disk surface; in a write operation, the write head flips the magnetization of the grains for each bit horizontally, parallel to the surface of the disk.
The write head typically comprises a pole tip, a yoke supporting the pole tip, and a conductive coil surrounding the yoke for electrically magnetizing the pole tip. During a write operation where the disk drive changes the storage state of a bit of data on the disk, the write head is moved to the location of the bit of data such that the pole tip is positioned directly above the bit, an electric current is passed through the coils to magnetize the pole tip, which in turn causes the magnetization of the bit to change.
In recent years, perpendicular recording has been introduced to achieve greater data storage density for disk drives. In perpendicular recording, the magnetization of each bit is aligned vertically, perpendicular to the disk surface. The write head flips the magnetization of the grains for each bit vertically, with either the north pole close to the surface or away from the surface. The perpendicular recording system allows more data bits per unit of disk surface area, which in turn enables greater data storage density for the disk drives.
A perpendicular recording system uses less disk surface area for each bit of data compared to a comparable longitudinal recording system. With the decease of surface area per bit of data, the dimensions of the pole tip of the write head must be reduced as well. A problem occurs when the magnetic state of the pole tip does not return to zero magnetization when the current in the conductive coils of the write head is stopped. This causes the pole tip to maintain some remnant magnetization field; and, as the write head moves across the disk, the pole tip can inadvertently change the magnetization state of other bits on the disk. This phenomenon is commonly known as pole tip erasure (PE) or pole tip lockup. Pole tip erasure (PE) can corrupt the data stored on the disk, and cause catastrophic failure for the disk drive.
There are several potential causes for the presence of remnant magnetic fields that cause pole tip erasure (PE) or pole tip lockup. One possible cause is the shape anisotropy of the pole tip. As the dimensions of the write pole tip decrease, the write pole tip becomes more similar in shape to a long-thin needle. The transverse self-demagnetizing field of the needle-like shape of the pole tip could potentially cause the magnetic domains of the pole tip to form into a lengthwise remnant magnetic state. That is, the magnetostatic energy is less when the magnetization is in the long axis of the needle compared to the short axis. Because it is easier to cause magnetization along the length direction of the tip compared to the transverse direction (hence the magnetic property is anisotropic), this shape anisotropy could potentially produce remnant magnetization in the pole tip even in the absence of an external field generated by the conductive coils.
Another possible cause of remnant magnetization in the pole tip is domain lockup of the yoke. The magnetization of the yoke may not immediately return to a zero-magnetization state after the current in the conductive coils is stopped; this in turn causes the pole tip to remain magnetized. A domain structure of the yoke with predominantly transverse magnetization will minimize domain lockup of the yoke. A domain structure with predominantly axial magnetization will enhance lockup of the yoke. Undesirable domain structures may be caused by axial magnetostriction anisotropy due to the interaction of the anisotropic stress field of the yoke with the magnetostriction of the yoke alloy.
In light of the problems discussed above, it is therefore preferable to have a write head design that eliminates or reduces the problem of pole tip lockup. Two methods of reducing the problem of remnant magnetization are proposed by Daniel Z. Bai and Jian-Gang Zhu, in “A Detached Pole Tip Design of Perpendicular Write Heads for High Data-Rate Recording”, IEEE Transactions on Magnetics, Vol. 38, No. 5, September 2002. One method is the insertion of a 10 nm gap, parallel to the air bearing surface (ABS), between the pole tip and the yoke. The second method is the insertion of a lamination layer throughout the pole tip and yoke to act as an anti-ferromagnetic coupling (AFC) layer.
Both methods proposed by Bai and Zhu are extremely difficult to manufacture in a manufacturing production process. Typically, the write head is manufactured in a process where the layers are deposited in planes perpendicular to the air-bearing-surface (ABS). Thus, the insertion of a gap parallel to the air bearing surface (ABS) near the pole tip requires the insertion of a very narrow (10 nm) but relatively deep (500 nm) gap in the pole tip area. The insertion of a gap with such dimensions and aspect-ratio cannot be practically achieved in a manufacturing process using the current state-of-the-art manufacturing techniques. The lamination method proposed by Bai and Zhu requires the insertion of a very thin (7 Å) layer in the middle of the deposition of the write yoke and write pole tip. Such a process step is expensive, time-consuming, difficult to control, and incompatible with electroplating manufacturing processes.
Therefore, it is a goal of embodiments of the present invention to create a write pole tip with reduced or eliminated pole-tip erasure (PE) characteristics utilizing current manufacturing methods.